Vue.js is one of very popular frameworks for building web apps or interactive web sites. Vue.js renders data to DOM declaretively and dynamically, so that makes creating interactive interfaces easier.
three.js is a 3D graphics library to use WebGL. It provides classes wrapping WebGL APIs, so that we can handle 3D objects intuitively.
They aim different targets to be rendered. Vue.js renders into DOM and three.js renderes into canvas.
Then VueGL bridge them! VueGL components render data to WebGL canvas declaretively and dynamically.